As magnetic resonance measuring devices, there are known a nuclear magnetic resonance (NMR) measuring device and an electron spin resonance (ESR) measuring device. As devices similar to the NMR measuring device, there is also known a magnetic resonance imaging (MRI) device. Hereinafter, the NMR measuring device will be explained.
The NMR is a phenomenon that a nucleus placed in a static magnetic field interacts with an electromagnetic wave having a natural frequency. The NMR measuring device measures a sample at an atomic level utilizing the phenomenon. The NMR measuring device is put to practical use in the analyzation of organic compounds (for example, chemicals, agricultural chemicals), high-polymer materials (for example, vinyl and polyethylene), biological materials (for example, nucleic acid or protein), and the like. By using the NMR measuring device, it is possible to determine a molecular structure of the sample, for example.
In the NMR measuring device, an NMR measuring probe (NMR signal detecting probe) is arranged together with the sample in a superconducting magnet generating a static magnetic field. The NMR measuring probe is provided with a coil for transmission and reception. The coil has a function of giving a variable magnetic field to the sample during the transmission and detecting an NMR signal of the sample during the reception. Since a resonance frequency differs depending upon a nucleic kind of an observed object, a high-frequency signal having a specific frequency adapted to the nucleic kind of the observed object is given to the coil during the sample measurement.
The cooling type NMR measuring probe is known as one kind of NMR measuring probe. In the cooling type NMR measuring probe, a vacuum vessel is used, and individual components (particularly in a detection system) in the vacuum vessel are placed in a low temperature state. An example of cooled target components present in the vacuum vessel may include a detection coil for detecting an NMR signal, and elements (a variable capacitor, a fixed capacitor, and the like) constituting a detection circuit. As a result of the cooling, an electrical resistance of the detection coil is decreased and a Q value is increased. In addition, an electrical heat noise is lowered. A high level of sensitivity is made possible by these effects. The sample itself is placed under atmospheric pressure (normal pressure), or under room temperature or temperature-controlled circumferences. In a device described in U.S. Pat. No. 7,378,847 or International Publication No. WO 2006/026541, a high vacuum is required as a vacuum degree in the vacuum vessel for avoiding vacuum discharge that may be generated in the detection coil.
In general, in the cooling type NMR measuring probe, a sample tube is accommodated in a gas pipe for sample temperature adjustment. The gas pipe for sample temperature adjustment is inserted in an outer wall body constituting the cooling type NMR measuring probe. Thereby a vacuum vessel is configured with the gas pipe for sample temperature adjustment and the outer wall body, and the vacuum vessel is reduced in internal pressure and cooled. A temperature in the gas pipe for sample temperature adjustment is maintained at room temperature. Alternatively, temperature adjustment gases are supplied into the gas pipe for sample temperature adjustment to control the internal temperature. A sealed section between the gas pipe for sample temperature adjustment and the outer wall body is generally sealed by a sealing member such as an O-ring made of a rubber material or the like, in consideration of limitation of amount space, assembly easiness of the probe, adjustment easiness thereof, and the like. The sealing member made of the rubber material is crushed in the sealed section by its elasticity, whereby a clearance in the sealed section is reduced to zero to realize the sealing. When the temperature adjustment gas is supplied to control a temperature in the gas pipe for sample temperature adjustment, a temperature of the sealing member also changes in response to this controlled temperature. When the gas pipe for sample temperature adjustment is internally cooled, the sealing member is also cooled, and when the gas pipe for sample temperature adjustment is internally heated, the sealing member is also heated.
In a case of controlling a sample temperature in the cooling type NMR measuring probe, it is preferable to be able to enlarge a possible temperature adjustment range of the temperature adjustment gas without deteriorating the vacuum degree in the vacuum vessel. For example, it is preferable that it is possible to lower the lower limit in the temperature adjustment range. However, in a case of using the sealing member made of the rubber material, it is difficult to lower the lower limit in the temperature adjustment range without deteriorating the vacuum degree. The cause of lowering the vacuum degree may generally include the following two causes. The first is, a sealing member embrittles to reduce elasticity of the sealing member and form a clearance in the sealed section, and a leak is generated through the clearance to lower the vacuum degree. The second is, in a case where a sealing member itself has a high gas permeability rate, a leak is generated through the sealing member to lower the vacuum degree.
As a sealing member low in a gas permeability rate, there is known a sealing member made of a fluorinated rubber material. Since the sealing member itself has a low gas permeability rate, it is possible to prevent or suppress a reduction in vacuum degree due to gas permeation. However, in a low temperature range (for example, in a range equal to −40° C. or less), the sealing member embrittles to lose elasticity, which causes lowering of the vacuum degree. As the sealing member that does not embrittle even in the low temperature region and maintains elasticity, there is known a sealing member made of a silicone rubber member. According to this sealing member, it is possible to prevent or suppress a reduction in vacuum degree due to the embrittlement of the sealing member in the low temperature region. However, since the sealing member itself has a high gas permeability rate in a regular temperature range (for example, −20° C. or more), the vacuum degree deteriorates in the regular temperature range.
As described above, it is difficult to realize both of the non-embrittlement of the sealing member in the low temperature region and the low gas permeability rate in the regular temperature region, and it is difficult to enlarge the temperature adjustment range without deteriorating the vacuum degree.
It is an advantage of the present disclosure to enlarge a possible temperature adjustment range of a temperature adjustment gas without deteriorating a vacuum degree within a vacuum vessel in an NMR measuring probe.